A phosphorylated nanocellulose/hydroxypropyl methylcellulose composite matrix: A biodegradable, flame-retardant and self-standing gel polymer electrolyte towards eco-friendly and high safety lithium ion batteries

Advances in the Study of Flame-Retardant Cellulose and Its Application in Polymers: A Review

Cellulose, as a green and renewable polymer material, has attracted the attention of a wide range of scholars for its excellent mechanical strength, easy chemical modification and degradability. However, its flammability limits its application in automotive, aerospace, construction, textile and electronic fields. This review recapitulates the modification methods of flame-retardant cellulose and their applications in polymers in recent years. This paper discusses the fabrication of flame-retardant cellulose from various aspects such as boron, nitrogen, phosphorus, sulphur, inorganic and heterogeneous synergistic modification, respectively, and evaluates the flame retardancy of flame-retardant cellulose by means of thermogravimetry, cone calorimetry, limiting oxygen index, the vertical combustion of UL94, etc. Finally, it discusses the application of flame-retardant cellulose in actual composites, which fully reflects the extraordinary potential of flame-retardant cellulose for applications in polymers. Currently, flame-retardant cellulose has significantly improved its flame-retardant properties through multi-faceted modification strategies and has shown a broad application prospect in composite materials. However, interfacial compatibility, environmental protection and process optimisation are still the key directions for future research, and efficient, low-toxic and industrialised flame-retardant cellulose materials need to be realised through innovative design.

Gel Polymer Electrolytes for Lithium Batteries: Advantages, Challenges, and Perspectives

The increasing demand for high-energy-density and safe lithium batteries has driven significant advancements in electrolyte technology. Among the various options, gel polymer electrolytes (GPEs) have emerged as a promising solution, combining the high ionic conductivity of liquid electrolytes with the structural integrity of solid-state (polymer) electrolytes. GPEs possess a hybrid structure composed of a polymer matrix, lithium salts, one or more solvents or plasticizers, and often functional additives, offering exceptional flexibility, adaptability, and performance for advanced energy storage systems. This review provides a comprehensive analysis of GPE technology for lithium batteries, covering fabrication methods, advantages, and challenges, while emphasizing potential application scenarios and the underlying mechanisms. Finally, future research directions are outlined to provide valuable insights and guidelines for advancing GPE technology.

Anisotropic Conductivity and Mechanical Strength Enhancements in Gel Polymer Electrolyte Films by Hot Pressing

Gel polymer electrolyte (GPE) with a polymer matrix swollen in liquid electrolytes offers several advantages over conventional liquid electrolytes, including no leakage, lightweight properties, and high reliability. While poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based GPEs show promise for lithium-ion batteries, their practical application is hindered by the intrinsic trade-off between ionic conductivity and mechanical robustness in conventional PVDF systems. Typical strategies relying on excessive plasticizers (e.g., ionic liquids) compromise mechanical integrity. Here, we propose a novel hot-pressing-induced recrystallization strategy to synergistically enhance both anisotropic ionic conductivity and puncture strength in PVDF-based GPE films. By blending PVDF with controlled amounts of 1-hexyl-3-methylimidazolium chloride ([HMIM]Cl), followed by solution casting and hot pressing, we achieve microstructural reorganization that dramatically improves through-thickness ion transport and mechanical performance. Crucially, hot-pressed PVDF with only 25 wt% [HMIM]Cl exhibits a 12.5-fold increase in ionic conductivity (reaching 4.7 × 10-4 S/cm) compared to its solution-cast counterparts. Remarkably, this formulation surpasses the conductivity of PVDF-HFP composites with a higher [HMIM]Cl content (35 wt%, 1.7 × 10-4 S/cm), demonstrating performance optimization of anisotropic conductivity. What is more, the mechanical strength of the piercing strength perpendicular to the GPE film after hot pressing increased by 42% compared to the solution-cast film. This work establishes a scalable processing route to break the conductivity-strength dichotomy in GPEs, offering critical insights for designing high-performance polymer electrolytes.

Biopolymer-Based Flame Retardants and Flame-Retardant Materials

Polymeric materials featuring excellent flame retardancy are essential for applications requiring high levels of fire safety, while those based on biopolymers are highly favored due to their eco-friendly nature, sustainable characteristics, and abundant availability. This review first outlines the pyrolysis behaviors of biopolymers, with particular emphasis on naturally occurring ones derived from non-food sources such as cellulose, chitin/chitosan, alginate, and lignin. Then, the strategies for chemical modifications of biopolymers for flame-retardant purposes through covalent, ionic, and coordination bonds are presented and compared. The emphasis is placed on advanced methods for introducing biopolymer-based flame retardants into polymeric matrices and fabricating biopolymer-based flame-retardant materials. Finally, the challenges for sustaining the current momentum in the utilization of biopolymers for flame-retardant purposes are further discussed.

Enhanced ionic conductivity and electrochemical performance of environmental friendly guar gum-based bio polymer gel electrolytes doped with Al2O3 nanofibers for Li-ion batteries

Recently, biopolymers made from natural resources are gaining popularity as polymer electrolytes (PEs) in electrochemical devices. In the present work, a series of guar gum (GG)-based biopolymer gel electrolytes (BGEs) filled with different amounts of Al2O3 nanofibers are synthesized and tested. The BGEs containing 7.5 wt% Al2O3 nanofibers show the maximum room temperature ionic conductivity of 2.37 × 10-3 S/cm at an uptake ratio of 120 %. Given the high conductivity, this uptake ratio is low, demonstrating that Al2O3 nanofibers affect GG's ion transport characteristics. XRD reveals that the Al2O3 in GG can create conductive environment for ion conduction. FTIR and XPS analyses demonstrate that nanofibers have the ability to generate supplementary routes for ion conduction in GG. Electrochemical investigations show that BGEs with 7.5 wt% nanofibers have a broad electrochemical potential range of 4.6 V. BGEs are stable at metallic electrodes and have a cationic transference number of 0.59. The initial discharge capacity at 0.5C has been measured to be 127 mAh g-1 for Li|BGE|LiFePO4 cell in the first cycle and 116 mAh g-1 with coulombic efficiency of over 94 % after 100 cycles. Nanofiber-dispersed BGEs have high thermal and mechanical stabilities, according to TGA, DSC, and UTM tests.

Eco-friendly methylcellulose/zinc alginate film with multi-function properties: thermal stability, flame retardancy and antibacterial activities

The purpose of this study was to synthesize crosslinked films from methylcellulose (MC) and sodium alginate (SA) using a straightforward ion exchange technique in a ZnCl2 coagulation bath. The resulting MC/ZA blend films exhibited significant improvements in thermal stability, with a measured increase of 191 °C in degradation temperature compared to MC film. The introduction of zinc ion (Zn2+) enhanced the flame retardancy of MC/ZA film, achieving a 92.4 % reduction in flammability. The microstructure of the MC/ZA blend film displayed a relatively smooth surface, indicating better biocompatibility between MC and ZA. Additionally, the barrier property of the MC/ZA film was improved, with a 35 % reduction in permeability to water vapor, and the mechanical properties were strengthened, showing a slightly reduction of 5 % in tensile strength. Furthermore, the MC/ZA blend film demonstrated enhanced antibacterial effectiveness, with a 99.99 % of S. aureus and E. coli, implying their suitability for packaging applications involving high oil content foods.

Lithium-Rich Porous Aromatic Framework Doped Quasi-Solid Polymer Electrolyte for Lithium Battery with High Cycling Stability

Lithium-ion batteries (LIBs) have revolutionized the energy storage landscape and are the preferred power source for various applications, ranging from portable electronics to electric vehicles. The constant drive and growth in battery research and development aim to enhance their performance, energy density, and safety. Advanced lithium batteries (LIBs) are considered to be the most promising electrochemical storage devices, which can provide high specific energy, volumetric energy density, and power density. However, the trade-off between ionic conductivity and cycling stability is still a major contradiction for SPEs. In this work, a novel hydroxylated PAF-1 was designed and synthesized through post-modification, and the lithium-rich single-ion porous aromatic framework PAF-1-OLi was thereafter prepared by lithiation, achieved with a specific surface area to be 155 m2 g-1 and a lithium content of 2.01 mmol g-1. PAF-1-OLi, lithium bis(trifluoromethanesulfony)limine (LiTFSI), and poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) were compounded to obtain PAF-1-OLi/PVDF by solution casting, which had good mechanical, thermodynamic, and electrochemical properties. The ion conductivity of PAF-1-OLi/PVDF infiltrated with plasticizer was 2.93 × 10-4 S cm-1 at 25 °C. The tLi+ was 0.77, which was much higher than that of the traditional dual-ion polymer electrolytes. The electrochemical window of PAF-1-OLi/PVDF can reach 4.9 V. The Li//PAF-1-OLi/PVDF//LiFePO4 battery initial discharge specific capacity was 147 mAh g-1 and reached 134.9 mAh g-1 after 600 cycles with a capacity retention rate of 91.2%, demonstrating its good cycling stability. The anionic part of lithium salt was fixed on the framework of PAF-1 to increase the Li+ transfer number of PAF-1-OLi/PVDF. The lithium-rich PAF-1-OLi and the LiTFSI provided abundant Li+ sources to transfer, while PAF-1-OLi helped to form a continuous Li+ transport channel, effectively promoting the migration of Li+ in the PAF-1-OLi/PVDF and effectively improving the Li+ conductivity. This study afforded a novel polymer electrolyte based on lithium-rich PAF-1-OLi, which has excellent electrochemical performance, providing a new choice for the polymer electrolyte of lithium batteries.

Graft onto approaches for nanocellulose-based advanced functional materials

The resurgence of cellulose as nano-dimensional 'nanocellulose' has unlocked a sustainable bioeconomy for the development of advanced functional biomaterials. Bestowed with multifunctional attributes, such as renewability and abundance of its source, biodegradability, biocompatibility, superior mechanical, optical, and rheological properties, tunable self-assembly and surface chemistry, nanocellulose presents exclusive opportunities for a wide range of novel applications. However, to alleviate its intrinsic hydrophilicity-related constraints surface functionalization is inevitably needed to foster various targeted applications. The abundant surface hydroxyl groups on nanocellulose offer opportunities for grafting small molecules or macromolecular entities using either a 'graft onto' or 'graft from' approach, resulting in materials with distinctive functionalities. Most of the reviews published to date extensively discussed 'graft from' modification approaches, however 'graft onto' approaches are not well discussed. Hence, this review aims to provide a comprehensive summary of 'graft onto' approaches. Furthermore, insight into some of the recently emerging applications of this grafted nanocellulose including advanced nanocomposite formulation, stimuli-responsive materials, bioimaging, sensing, biomedicine, packaging, and wastewater treatment has also been reviewed.

Cross-Linking of Sugar-Derived Polyethers and Boronic Acids for Renewable, Self-Healing, and Single-Ion Conducting Organogel Polymer Electrolytes

This report describes the synthesis and characterization of organogels by reaction of a diol-containing polyether, derived from the sugar d-xylose, with 1,4-phenylenediboronic acid (PDBA). The cross-linked materials were analyzed by infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), scanning electron microscopy (FE-SEM), and rheology. The rheological material properties could be tuned: gel or viscoelastic behavior depended on the concentration of polymer, and mechanical stiffness increased with the amount of PDBA cross-linker. Organogels demonstrated self-healing capabilities and recovered their storage and loss moduli instantaneously after application and subsequent strain release. Lithiated organogels were synthesized through incorporation of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into the cross-linked matrix. These lithium-borate polymer gels showed a high ionic conductivity value of up to 3.71 × 10^-3 S cm^-1 at 25 °C, high lithium transference numbers (t ₊ = 0.88-0.92), and electrochemical stability (4.51 V). The gels were compatible with lithium-metal electrodes, showing stable polarization profiles in plating/stripping tests. This system provides a promising platform for the production of self-healing gel polymer electrolytes (GPEs) derived from renewable feedstocks for battery applications.